The present invention relates to a photographic flash circuit, and, more particularly to a flash circuit having a voltage boosting circuit for charging a photoflash capacitor.
It is well known to use electronic flash circuits to provide artificial illumination of a scene to improve the appearance of a photographic image. Because cameras are typically portable many electronic flash circuits draw energy from portable batteries such as chemical batteries. Charging circuits are used to convert battery voltage into a higher voltage that can charge a flash capacitor so that it stores sufficient energy to cause a flash tube to discharge enough light to illuminate the scene. Chemical batteries provide a fixed amount of power to such flash circuits and, therefore, needless operation of the flash charging circuit is to be avoided to prevent premature exhaustion of the chemical batteries during a photography session.
U.S. Pat No. 4,522,479 entitled xe2x80x9cFlash Apparatus with Power Supply Control Devicexe2x80x9d filed in the name of Yamada et al. on Dec. 24, 1983 discloses a power supply control device for use in a flash apparatus. The disclosed power supply control device automatically cuts off power to a flash apparatus by turning off a power switch at a predetermined time after the power switch is turned xe2x80x9conxe2x80x9d. This prevents the waste of electrical energy that can arise from, for example, the careless failure to turn the power switch off. The power supply control device is provided with a timer circuit that sets the predetermined period of time and is arbitrarily resettable with a manually operable power switch. The circuit of the ""479 patent incorporates a number of expensive electrical components, including integrated circuits such as operational amplifiers and a one shot multivibrator. This makes such a circuit expensive. This circuit may be useful for flash circuits of the type that are incorporated in expensive products such as single lens reflex cameras and separable flash units of the type that are typically used with SLR type cameras. What is needed is a less expensive circuit for use in lower cost cameras and one-time use cameras.
A flash circuit for use in a camera, the flash charging circuit comprising a flash light discharge circuit having a light emitting element electrically connected to a flash capacitor; a flash triggering circuit connected to the flash light discharge circuit with the flash triggering circuit having a trigger signal generating circuit generating a signal that enables energy from the energy storage device to be converted into light by the light emitting element; a voltage conversion circuit connected between a battery and the flash capacitor to convert energy from a source voltage into a higher voltage to charge the flash capacitor; a timer circuit to cause the voltage conversion circuit to operate when the voltage at a timing capacitor is within a range of voltages, said timer circuit incorporating said timing capacitor in a time constant circuit that discharges energy stored in the timing capacitor at a predetermined rate; a reset circuit that resets the timing capacitor voltage to a voltage that is within the range; wherein the range of voltages is higher than the battery voltage and wherein the reset circuit first applies battery voltage to the timing capacitor and then applies voltage generated by the voltage conversion circuit to charge the timing capacitor to a voltage that is higher than the battery voltage.
A flash charging circuit for use in a camera, the flash charging circuit comprising a flash light discharge circuit comprising a light emitting element electrically connected to a flash capacitor; a flash triggering circuit connected to the flash light discharge circuit with the flash triggering circuit having a trigger signal generating circuit generating a signal that enables energy from the flash capacitor to be converted into light by the light emitting element;
a voltage conversion circuit connected between a battery and the flash capacitor to convert energy from a battery voltage into a higher voltage to charge the flash capacitor; a timer circuit to cause the voltage conversion circuit to operate when the voltage at a timing capacitor is within a range of voltages, said timer circuit incorporating the timing capacitor in a time constant circuit that discharges energy stored in the timing capacitor at a predetermined rate; and a reset circuit having a thyristor connected to the timing capacitor, a gate of said thyristor being triggered upon operation of a shutter of the camera, with the thyristor being connected to the battery and conducting energy from the battery to the timing capacitor when the thyristor is triggered to charge the timing capacitor to a voltage no greater than the battery voltage but within the range of voltages; wherein said voltage conversion circuit further supplies voltage pulses to the thyristor to charge the timing capacitor to a voltage higher than the battery voltage when the voltage conversion circuit is operated and wherein the thyristor turns off when the voltage at the timing capacitor approaches the voltage of said pulses.
In yet another aspect of the invention, what is provided is a photographic flash circuit The flash circuit has a light emitting element connected to a flash capacitor, a flash triggering circuit which causes the light emitting element to convert energy from the flash capacitor into light and a voltage conversion circuit for converting a low battery voltage into a higher voltage to charge said flash capacitor, with the voltage conversion circuit having an oscillation transistor and at least one other transistor in an oscillation current path, said oscillation transistor oscillating during voltage conversion. A diode is connected to more than one transistor to suppress any voltage spikes at both transistors that appear during oscillation at the transistors to which the diode is connected.
In still another aspect of the invention a photographic flash charging circuit is provided. The photographic flash circuit comprises a light emitting element connected to a flash capacitor, a flash triggering circuit which causes the light emitting element to convert energy from the energy storage capacitor into light, and a timer control circuit adapted to cause the voltage conversion circuit to operate for a timing period and then automatically shut off, with the timer control being reset to the beginning of the timing period by actuation of the flash triggering circuit, with the timer control circuit having a timing period determined as a function of the voltage to which a timing capacitor is charged when the timer control circuit is reset. Test points are provided across the timing capacitor so that a testing circuit can determine conditions at the timing capacitor during the testing.